Boost dc-dc converter and method of using the same

ABSTRACT

A boost DC-DC converter includes: an input terminal; an output terminal; a first boost circuit configured to generate, from an input power to the input terminal, a first boosted power having a higher voltage than a voltage of the input power, and outputs the generated first boosted power from the output terminal; a second boost circuit configured to generate, from the input power, a second boosted power having a higher voltage than the voltage of the input power; and a storage capacitor configured to store the second boosted power as a storage power, and supply the storage power to the first boost circuit as an operation power source. The first boost circuit is configured to start a boost operation with the storage power when a voltage of the storage power is equal to or higher than a minimum operation voltage of the first boost circuit.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to JapanesePatent Application No. 2016-243695 filed on Dec. 15, 2016, the entirecontent of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a boost DC-DC converter and a method ofusing the same.

2. Description of the Related Art

A boost DC-DC converter having an input terminal and an output terminalhas been known (for example, refer to Japanese Unexamined PatentApplication No. 2009-254110).

FIG. 3 is a schematic circuit diagram of a conventional boost DC-DCconverter 300. In an example of FIG. 3, an output terminal 314 of theboost DC-DC converter 300 is connected to a ground terminal via a load400. The boost DC-DC converter 300 boosts input power input from aninput terminal 301 and supplies the boosted power to the load 400.

In the example of FIG. 3, the boost DC-DC converter 300 generates theboosted power having higher voltage than that of the input power fromthe input power supplied to the input terminal 301, and the boost DC-DCconverter 300 outputs the generated boosted power from the outputterminal 314.

The boost DC-DC converter 300 includes a coil 302, an N-channel MOStransistor 305, a diode 303, a diode 304, a diode 321, an outputcapacitor 311, a resistor 312, a resistor 313, and a control circuit307.

One terminal of the coil 302 is connected to the input terminal 301. TheN-channel MOS transistor 305 switches current which flows from the otherterminal of the coil 302 to a ground terminal. The diode 303 rectifiesthe current output from the other terminal of the coil 302 and outputsthe boosted power. An N-type terminal of the diode 303 is connected tothe output terminal 314. The N-type terminal of the diode 303 isconnected to a ground terminal via the output capacitor 311. The N-typeterminal of the diode 303 is connected to a ground terminal via theresistor 312 and the resistor 313. The N-type terminal of the diode 303is connected to a power source terminal 309 of the control circuit 307via the diode 321.

The diode 304 rectifies the current input from the input terminal 301,and the diode 304 outputs the input power to the power source terminal309 of the control circuit 307 as an operation power source of thecontrol circuit 307. The other terminal of the coil 302 and a drain ofthe N-channel MOS transistor 305 are connected to each other.

The control circuit 307 includes a switching signal output terminal 308,the power source terminal 309, and a feedback terminal 310. Theswitching signal output terminal 308 outputs a switching signal fordriving the N-channel MOS transistor 305 to the gate of the N-channelMOS transistor 305. The source of the N-channel MOS transistor 305 isconnected to the ground terminal. The N-type terminal of the diode 303is connected to the feedback terminal 310 via the resistor 312. Thecontrol circuit 307 controls the boosted power by controlling theN-channel MOS transistor 305 based on the input of the feedback terminal310.

In the example of FIG. 3, when input power is supplied to the inputterminal 301, the input power is input to the power source terminal 309of the control circuit 307 via the diode 304. The control circuit 307starts an operation by the input power supplied to the power sourceterminal 309. Specifically, the control circuit 307 outputs theswitching signal from the switching signal output terminal 308, andswitches the N-channel MOS transistor 305.

When the control circuit 307 switches on the N-channel MOS transistor305, power is stored in the coil 302. When the control circuit 307switches off the N-channel MOS transistor 305, the power stored in thecoil 302 is output to the output terminal 314 via the diode 303. Theboost DC-DC converter 300 generates the boosted power and outputs theboosted power from the output terminal 314 by repeating poweraccumulation and power discharge performed by the coil 302.

In the example of FIG. 3, when the boosted power is generated at theoutput terminal 314, the boosted power is supplied to the power sourceterminal 309 of the control circuit 307 via the diode 321. Accordingly,the control circuit 307 which generated the boosted power using theinput power as the operation power source, generates the boosted powerusing the boosted power as the operation power source.

The voltage of the output terminal 314 is divided by the resistor 312and the resistor 313, and is input to the feedback terminal 310 of thecontrol circuit 307. The control circuit 307 controls the switching ofthe N-channel MOS transistor 305 such that the voltage of the feedbackterminal 310 becomes a predetermined value, thereby controlling thevoltage of the output terminal 314 to a desired value.

In the example of FIG. 3, the diode 304 is provided to use the inputvoltage to operate the control circuit 307 with a small loss of voltage,thereby reducing a value of the input voltage required to activate thecontrol circuit 307 compared to a case without the diode 304. And thediode 321 is provided to use the boosted power having higher voltagethan that of the input power as the operation power source of thecontrol circuit 307 after the control circuit 307 is activated, therebyincreasing power conversion capability.

However, in the conventional boost DC-DC converter as described above,when the voltage of the input power is lower than a minimum operationvoltage of the control circuit, the control circuit cannot startoperation, neither start boost operation.

When the voltage of the input power is low, the voltage of the boostedpower also becomes low. A power conversion amount thus decreases. When aload of large power consumption is connected to the output terminal, theconventional boost DC-DC converter, thus, cannot raise the voltage ofthe output terminal to a desired voltage and fails to activate the loadsince the boosted power falls short of the power consumption of the loadat the activation from an input power having a low voltage.

The conventional boost DC-DC converter should have a configurationhaving a very large conversion capability to activate the load from theinput power having a low voltage when the load of large powerconsumption is connected to the output terminal, resulting in increaseof a size of the entire DC-DC converter and also increase of a powerconversion loss.

An object of the present invention is to provide a boost DC-DC converterin which a boost operation can be started even when voltage of inputpower becomes low, and a method of using the same.

SUMMARY OF THE INVENTION

In order to achieve the above described object, the present inventionadopts the following aspects.

(1) According to an aspect of the present invention, there is provided aboost DC-DC converter including: an input terminal; an output terminal;a first boost circuit configured to generate, from an input power to theinput terminal, a first boosted power having a higher voltage than avoltage of the input power, and outputs the generated first boostedpower from the output terminal; a second boost circuit configured togenerate, from the input power, a second boosted power having a highervoltage than the voltage of the input power; and a storage capacitorconfigured to store the second boosted power as a storage power, andsupply the storage power to the first boost circuit as an operationpower source of the first boost circuit, the first boost circuit beingconfigured to start a boost operation with the storage power as theoperation power source when a voltage of the storage power is equal toor higher than a minimum operation voltage of the first boost circuit.

(2) In the boost DC-DC converter according to the above (1), thefollowing configuration may be configured: the first boost circuitincludes a coil having a terminal connected to the input terminal, anN-channel MOS transistor configured to switch a current flowing from theother terminal of the coil to a ground terminal, a first rectifierconfigured to rectify a pulse current output from the other terminal tooutput the first boosted power, a second rectifier configured to connectto the first rectifier in parallel, and rectifies the pulse current tooutput a third boosted power, and a control circuit to which the thirdboosted power is input and configured to control the first boosted powerby controlling the N-channel MOS transistor, wherein the first boostcircuit is configured to perform the boost operation with the thirdboosted power as the operation power source when a voltage of the thirdboosted power is equal to or higher than the minimum operation voltage.

(3) According to another aspect of the present invention, there isprovided a method of using the boost DC-DC converter according to theabove (1), comprising: driving a load connected to the output terminalby the first boosted power output from the output terminal, wherein thefirst boosted power is equal to or higher than a power consumption ofthe load.

(4) According to further another aspect of the present invention, thereis provided a method of using the boost DC-DC converter according to theabove (2), comprising: driving a load connected to the output terminalby the first boosted power output from the output terminal, wherein thefirst boosted power is equal to or higher than a power consumption ofthe load.

According to the above-described aspects of the present invention, it ispossible to provide a boost DC-DC converter in which a boost operationcan be started even when the voltage of input power is low, and a methodof using the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a FIG. 1 is a schematic circuit diagram of a boost DC-DCconverter according to the first embodiment of the present invention.

FIG. 2 is a diagram showing an example of an operation waveform of theboost DC-DC converter of the first embodiment.

FIG. 3 is a schematic circuit diagram of a conventional boost DC-DCconverter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Hereinafter, the first embodiment of a boost DC-DC converter 100 isdescribed with reference to the drawings.

FIG. 1 is a schematic circuit diagram of the boost DC-DC converter 100according to the first embodiment. In the example of FIG. 1, an outputterminal 114 of the boost DC-DC converter 100 according to the firstembodiment is connected to a load 200. More specifically, the outputterminal 114 is connected to a ground terminal via the load 200. In thisexample, the load 200 is a wireless communication module. In this case,the boost DC-DC converter 100 boosts input power input from an inputterminal 101 and supplies the boosted input power to the wirelesscommunication module. In another example, the load 200 other than thewireless communication module may be connected to the output terminal114 of the boost DC-DC converter 100.

The boost DC-DC converter 100 of the first embodiment includes a firstboost circuit 100 a, a second boost circuit 115, and a storage capacitor116. The first boost circuit 100 a generates the first boosted powerhaving higher voltage than voltage of the input power from the inputpower input to the input terminal 101, and the first boost circuit 100 aoutputs the generated first boosted power from the output terminal 114.The second boost circuit 115 generates the second boosted power havinghigher voltage than voltage of the input power from the input powerinput to the input terminal 101, and the second boost circuit 115outputs the generated second boosted power from an output terminal 120of the second boost circuit 115. The storage capacitor 116 stores thesecond boosted power generated by the second boost circuit 115 asstorage power. The storage capacitor 116 supplies the stored storagepower to a power source terminal 109 of a control circuit 107 of thefirst boost circuit 100 a as an operation power source of the controlcircuit 107 of the first boost circuit 100 a.

In the example of FIG. 1, the first boost circuit 100 a includes a coil102, an N-channel MOS transistor 105, a diode 103 which serves as firstrectifier, a diode 104 which serves as second rectifier, a smoothingcapacitor 106, an output capacitor 111, a resistor 112 and a resistor113 which configure a bleeder resistor, and a control circuit 107.

In the example of FIG. 1, the N-channel MOS transistor 105 is applied tothe boost DC-DC converter 100. However, the present invention is notlimited to this configuration only. In another example, instead of theN-channel MOS transistor 105, an arbitrary switching element (not shown)may be applied to the boost DC-DC converter 100.

In the example of FIG. 1, one terminal (left one shown in FIG. 1) of thecoil 102 is connected to the input terminal 101. The N-channel MOStransistor 105 switches current which flows from the other terminal(right one shown in FIG. 1) of the coil 102 to a ground terminal. Thediode 103 rectifies a pulse current output from the other terminal ofthe coil 102 and the diode 103 outputs the first boosted power. Theother terminal of the coil 102 and a P-type terminal of the diode 103are connected to each other. An N-type terminal of the diode 103 isconnected to the output terminal 114. The N-type terminal of the diode103 is connected to a ground terminal via the output capacitor 111. TheN-type terminal of the diode 103 is connected to a ground terminal viathe resistor 112 and the resistor 113 forming the bleeder resistor.

The diode 104 is connected to the other terminal of the coil 102 so asto be in parallel with the diode 103. The diode 104 outputs thirdboosted power obtained by rectifying the pulse current output from theother terminal of the coil 102 to the power source terminal 109 of thecontrol circuit 107 as the operation power source of the control circuit107. The other terminal of the coil 102 and a P-type terminal of thediode 104 are connected to each other. An N-type terminal of the diode104 is connected to the power source terminal 109. The N-type terminalof the diode 104 is connected to a ground terminal via the smoothingcapacitor 106. The other terminal of the coil 102 and the drain of theN-channel MOS transistor 105 are connected to each other.

In the example of FIG. 1, the control circuit 107 includes a switchingsignal output terminal 108, the power source terminal 109, and afeedback terminal 110. The switching signal output terminal 108 outputsa switching signal for driving the N-channel MOS transistor 105 to thegate of the N-channel MOS transistor 105. The gate of the N-channel MOStransistor 105 is connected to the switching signal output terminal 108.The source of the N-channel MOS transistor 105 is connected to a groundterminal. The N-type terminal of the diode 103 is connected to thefeedback terminal 110 via the resistor 112 forming a portion of thebleeder resistor. The control circuit 107 controls the first boostedpower by controlling the N-channel MOS transistor 105 based on the inputof the feedback terminal 110.

In the example of FIG. 1, the boost DC-DC converter 100 includesswitching element 117. The second boost circuit 115 includes an inputterminal 118, a switching signal output terminal 119, and an outputterminal 120. The input terminal 118 of the second boost circuit 115 isconnected to the input terminal 101. The output terminal 120 isconnected to a ground terminal via the storage capacitor 116. The outputterminal 120 is connected to the power source terminal 109 of thecontrol circuit 107 of the first boost circuit 100 a via the switchingelement 117. The N-type terminal of the diode 104 is connected to aground terminal via the switching element 117 and the storage capacitor116. The N-type terminal of the diode 104 is connected to the outputterminal 120 of the second boost circuit 115 via the switching element117. The switching signal output terminal 119 of the second boostcircuit 115 is connected to the switching element 117. The switchingsignal output terminal 119 outputs a switching signal for driving theswitching element 117 to the switching element 117. In this example ofFIG. 1, the switching element 117 is a switching device such as theN-channel MOS transistor.

In this example, as the second boost circuit 115, a flying capacitorboost circuit, a charge pump boost circuit incorporating a boostcapacitor, or the like can be used.

In the boost DC-DC converter 100 of the first embodiment, when thevoltage of the storage power stored in the storage capacitor 116 isequal to or higher than the minimum operation voltage of the first boostcircuit 100 a, the first boost circuit 100 a starts a boost operationwith the storage power as the operation power source.

In the example of FIG. 1, when the voltage of the storage power is equalto or higher than the minimum operation voltage of the control circuit107 of the first boost circuit 100 a, the second boost circuit 115 turnson the switching element 117. As a result, the storage power is suppliedto the control circuit 107, and thus, the control circuit 107 enters astate in which the control circuit 107 can switch the N-channel MOStransistor 105 with the storage power as the operation power source.Next, the control circuit 107 starts switching of the N-channel MOStransistor 105. Thus, the first boost circuit 100 a starts the boostoperation.

When the voltage of the third boosted power output from the diode 104 isequal to or higher than the minimum operation voltage, the controlcircuit 107 enters a state in which the control circuit 107 can switchthe N-channel MOS transistor 105 by using the third boosted powersupplied to the control circuit 107. When the voltage of the thirdboosted power is equal to or higher than the minimum operation voltage,the first boost circuit 100 a performs the boost operation with thethird boosted power as the operation power source.

FIG. 2 is a diagram showing an example of an operation waveform of theboost DC-DC converter 100 of the first embodiment. A horizontal axis inFIG. 2 indicates time. A vertical axis in (A) of FIG. 2 indicates thevoltage of the input terminal 101. A vertical axis in (B) of FIG. 2indicates the voltage of the power source terminal 109 of the controlcircuit 107. A vertical axis in (C) of FIG. 2 indicates the voltage ofthe output terminal 114. A vertical axis in (D) of FIG. 2 indicates thevoltage of the storage power stored by the storage capacitor 116. Avertical axis in (E) of FIG. 2 indicates the voltage of the thirdboosted power output from the diode 104 of the first boost circuit 100a.

In the example of FIG. 2, at time t1, the input power is supplied to theinput terminal 101 and the voltage of the input terminal 101 becomes avalue V1. The input power supplied to the input terminal 101 is suppliedto the input terminal 118 of the second boost circuit 115. The secondboost circuit 115 generates the second boosted power having a value V4which is a higher voltage than the value V1 of the voltage of the inputpower, from the input power. The second boost circuit 115 outputs thesecond boosted power to the output terminal 120. The second boostedpower output from the output terminal 120 is stored in the storagecapacitor 116 as the storage power. Accordingly, after time t1, thevoltage of the storage power gradually increases. The second boostcircuit 115 monitors the voltage (the voltage of the storage powerstored in the storage capacitor 116) of the output terminal 120.

At time t1, the first boost circuit 100 a has not yet started the boostoperation. Accordingly, the value of the first boosted power generatedby the first boost circuit 100 a becomes zero. The value of the voltageof the third boosted power output from the diode 104 becomes zero.

At time t1, a value Vout1 of the voltage of the output terminal 114 islower than the value V1 of the voltage of the input terminal 101 by aforward voltage drop in the diode 103.

At time t1, the second boost circuit 115 does not turn on the switchingelement 117. At time t1, the switching element 117 is in a turned-offstate. Accordingly, the second boosted power generated by the secondboost circuit 115 is not supplied to the power source terminal 109 ofthe control circuit 107. As a result, a value V2 of the voltage in thepower source terminal 109 of the control circuit 107 is lower than thevalue V1 of the voltage of the input terminal 101 by a forward voltagedrop in the diode 104.

In the example of FIGS. 1 and 2, the forward voltage drop in the diode104 is smaller than the forward voltage drop in the diode 103.Accordingly, the value V2 of the voltage of the power source terminal109 of the control circuit 107 is higher than the Vout1 of the voltageof the output terminal 114 at time t1.

Subsequently, in the example of FIG. 2, at time t2, the voltage of thestorage power reaches a minimum operation voltage VT of the controlcircuit 107 of the first boost circuit 100 a. At time 2, when thestorage power is supplied to the power source terminal 109 of thecontrol circuit 107, the control circuit 107 enters a state in which thecontrol circuit 107 can output the switching signal to the N-channel MOStransistor 105. In the example of FIG. 2, at time t2, the storage powerhas not yet supplied to the power source terminal 109 of the controlcircuit 107.

Subsequently, in the example of FIG. 2, at time t3, the voltage of thestorage power becomes equal to a value V4 of the voltage of the secondboosted power generated by the second boost circuit 115. The value V4 ishigher than the minimum operation voltage VT.

At time t3, the second boost circuit 115 stops the boost operation andturns on the switching element 117. Accordingly, the storage power issupplied to the power source terminal 109 of the control circuit 107 viathe switching element 117. As a result, the voltage of the power sourceterminal 109 of the control circuit 107 becomes higher than the minimumoperation voltage VT. Accordingly, the control circuit 107 can switchthe N-channel MOS transistor 105 with the storage power as the operationpower source. The switching signal output terminal 108 of the controlcircuit 107 outputs the switching signal for driving the N-channel MOStransistor 105 to the gate of the N-channel MOS transistor 105.

The example of FIG. 2, at time t3, the control circuit 107 starts theswitching of the N-channel MOS transistor 105.

More specifically, when the control circuit 107 turns on the N-channelMOS transistor 105, power is stored in the coil 102. When the controlcircuit 107 turns off the N-channel MOS transistor 105, the power storedin the coil 102 is output to the output terminal 114 via the diode 103.The first boost circuit 100 a repeats power accumulation and powerdischarge performed by the coil 102 to generate the first boosted power.

At time t3, the first boost circuit 100 a starts the boost operation ofgenerating the first boosted power with the storage power as theoperation power source. Accordingly, at time t3, the first boosted powerbecomes larger than zero. The first boosted power is output to theoutput terminal 114 via the diode 103. Accordingly, the voltage of theoutput terminal 114 increases from the value Vout1 to a value Vout2.

The voltage of the output terminal 114 is divided by the resistor 112and the resistor 113 and is input to the feedback terminal 110 of thecontrol circuit 107.

After the boost operation of the first boost circuit 100 a is started(after time t3), the control circuit 107 controls the switching of theN-channel MOS transistor 105 such that the voltage of the feedbackterminal 110 becomes a predetermined value. Accordingly, the controlcircuit 107 controls the voltage of the output terminal 114 to thedesired value Vout2.

After time t3, a portion of the power stored in the coil 102 is outputfrom the diode 104 to the power source terminal 109 of the controlcircuit 107 as the third boosted power. The value V3 of the voltage ofthe power source terminal 109 is higher than the minimum operationvoltage VT.

Accordingly, after time t3, the control circuit 107 switches theN-channel MOS transistor 105 with the third boosted power as theoperation power source. The first boost circuit 100 a performs the boostoperation, which generates the first boosted power, with the thirdboosted power as the operation power source.

As described above, after time t3, the first boost circuit 100 aperforms the boost operation, which generates the first boosted power,with the third boosted power as the operation power source. Accordingly,the second boosted power is not required. Therefore, in the example ofFIG. 2, after time t3, the second boost circuit 115 does not generatethe second boosted power.

The turned-on state of the switching element 117 is maintained.Accordingly, the value of the voltage of the storage power becomes equalto the value V3 of the voltage of the power source terminal 109.

In the example of FIGS. 1 and 2, as described above, the forward voltagedrop in the diode 104 is lower than the forward voltage drop in thediode 103. Accordingly, the value V3 of the voltage of the power sourceterminal 109 of the control circuit 107 after time t3 is higher than thevalue Vout2 of the voltage of the output terminal 114 after time t3.

As described above, in the boost DC-DC converter 100 of the firstembodiment, when the voltage of the storage power is equal to or higherthan the minimum operation voltage VT of the first boost circuit 100 a,the first boost circuit 100 starts the boost operation with the storagepower as the operation power source. Accordingly, it is possible tostart the boost operation of the first boost circuit 100 a even when thevoltage of the input power is low. The boost capability required in thesecond boost circuit 115 can be suppressed comparing with the examplewhen the storage capacitor 116 is not provided.

As described above, in the example of FIG. 2, after time t3, the secondboost circuit 115 does not generate the second boosted power.Accordingly, it is possible to eliminate the necessity of controllingthe second boost circuit 115 after time t3 when the voltage of the thirdboosted power becomes the value V3 equal to or higher than the minimumoperation voltage VT.

As described above, in the example of FIG. 1, the output terminal 114 ofthe boost DC-DC converter 100 is connected to the load 200. The firstboosted power output from the output terminal 114 drives the load 200.In the example of FIG. 2, after time t3, the first boosted power becomesa value equal to or higher than the power consumption of the load 200.

In the example of FIG. 2, even when the power of the input power is low,the first boost circuit 100 a can start the boost operation with thestorage power having higher voltage than the voltage of the input poweras the operation power source. When the boost operation is started (timet3), the first boosted power (conversion power) exceeds the powerconsumption of the load 200. The boost DC-DC converter 100 outputs thefirst boosted power (conversion power) exceeding the power consumptionof the load 200 by the input of the input power having a lower voltagethan the minimum operation voltage VT. In the boost DC-DC converter 100,the size thereof is small and the conversion loss thus becomes lower.

The second boost circuit 115 needs to be a circuit which has a lowerminimum operation voltage than that of the first boost circuit 100 a andcan boost even when the input voltage is low, and the power conversioncapability of the second boost circuit 115 may be smaller than that ofthe first boost circuit 100 a. Accordingly, the size of the second boostcircuit 115 can be decreased.

In the example of the conventional circuit of FIG. 3, the controlcircuit 307 switches the N-channel MOS transistor 305 with boosted powerhaving voltage decreased by a forward voltage drop in the diode 303 andthe diode 321 as an operation power source. On the other hand, in theexample of the first embodiment of FIG. 1, the control circuit 107switches the N-channel MOS transistor 105 with the third boosted powerhaving the voltage decreased by only the forward voltage drop in thediode 104 as the operation power source. Accordingly, compared to theexample of the conventional circuit of FIG. 3, in the example of thefirst embodiment of FIG. 1, it is possible to adopt a configuration inwhich the first boosted power (conversion power) is small, the sizethereof can be decreased, and the conversion loss can be decreased.

In the example of FIG. 2, the second boosted power generated by thesecond boost circuit 115 is stored in the storage capacitor 116. Whenthe voltage of the storage power stored in the storage capacitor 116 isequal to or higher than the minimum operation voltage VT of the firstboost circuit 100 a, the control circuit 107 starts the boost operationby the first boost circuit 100 a with the storage power as the operationpower source. Accordingly, unlike the example of the conventionalcircuit of FIG. 3, in the example of the first embodiment of FIG. 2, itis not necessary to drive the control circuit with the boosted power asthe operation power source. In the example of the first embodiment ofFIG. 2, even when the boost capability of the second boost circuit 115is low, it is possible to drive the control circuit 107 by taking timesto store electricity. Accordingly, it is possible to decrease the sizeof the second boost circuit 115.

In the example of FIG. 1, the diode 103 is used as the first rectifierand the diode 104 is used as the second rectifier, the present inventionis not limited to this configuration only. In another example, insteadof the diode, an arbitrary element, a circuit, or the like having arectification function may be used.

Second Embodiment

In a boost DC-DC converter 100 of the second embodiment is configured tobe similar to the boost DC-DC converter 100 of the above-described firstembodiment except for the following matters. Therefore, according to theboost DC-DC converter 100 of the second embodiment, advantageous effectssimilar to those of the boost DC-DC converter 100 of the firstembodiment can be exerted.

As of FIG. 1, the first boost circuit 100 a of the boost DC-DC converter100 of the above-described first embodiment is a boost chopper typevoltage conversion circuit. On the other hand, in the boost DC-DCconverter 100 of the second embodiment, in this example, anotherarbitrary voltage conversion circuit (not shown) such as a charge pumptype voltage conversion circuit can be used as the first boost circuit100 a.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Theseembodiments and modifications can be performed in other various ways;therefore, additions, omissions, substitutions, and other modificationscan be made without departing from the scope of the invention. Theseembodiments and modifications are included in the scope of the inventiondescribed in the claims and equivalence thereof. Furthermore, theembodiments and the modifications can be combined with each other.

What is claimed is:
 1. A boost DC-DC converter comprising: an inputterminal; an output terminal; a first boost circuit configured togenerate, from an input power to the input terminal, a first boostedpower having a higher voltage than a voltage of the input power, andoutputs the generated first boosted power from the output terminal; asecond boost circuit configured to generate, from the input power, asecond boosted power having a higher voltage than the voltage of theinput power; and a storage capacitor configured to store the secondboosted power as a storage power, and supply the storage power to thefirst boost circuit as an operation power source of the first boostcircuit, the first boost circuit being configured to start a boostoperation with the storage power as the operation power source when avoltage of the storage power is equal to or higher than a minimumoperation voltage of the first boost circuit.
 2. The boost DC-DCconverter according to claim 1, wherein the first boost circuit includesa coil having a terminal connected to the input terminal, an N-channelMOS transistor configured to switch a current flowing from the otherterminal of the coil to a ground terminal, a first rectifier configuredto rectify a pulse current output from the other terminal to output thefirst boosted power, a second rectifier configured to connect to thefirst rectifier in parallel, and rectifies the pulse current to output athird boosted power, and a control circuit to which the third boostedpower is input and configured to control the first boosted power bycontrolling the N-channel MOS transistor, wherein the first boostcircuit is configured to perform the boost operation with the thirdboosted power as the operation power source when a voltage of the thirdboosted power is equal to or higher than the minimum operation voltage.3. A method of using the boost DC-DC converter according to claim 1,comprising: driving a load connected to the output terminal by the firstboosted power output from the output terminal, wherein the first boostedpower is equal to or higher than a power consumption of the load.
 4. Amethod of using the boost DC-DC converter according to claim 2,comprising: driving a load connected to the output terminal by the firstboosted power output from the output terminal, wherein the first boostedpower is equal to or higher than a power consumption of the load.